The non-destructive nature of optical methods makes them very important tools in investigating thin films. Several interferometric and ellipsometric tools are widely used for thin film thickness measurement in industry and basic science (on ellipsometry see, for example: M. Steinberg et al, A New Method for Measurement on Surfaces and
Surface Layers, Mater. Sci. and Eng., 1980, 42, 65–69. D. Beaglehole, H. K. Christenson, “Vapour adsorption on mica and silicon-entropy effects, layering and surface forces”, J.Phys.Chem., 96, 3395–3403, (1992). D. Beaglehole, “Performance of a microscopic imaging ellipsometer”, Rev.Sci.Instrum., 59, 2557, (1998)). The typical thickness of films in microelectronics varies in the range of 0÷10 μm. The development of faster microelectronic devices demands development of very thin film technology and therefore new characterization methods of thin films are needed. Recent investigations of thin film stability involve understanding the influence of entropy effects on molecular scales. In the field of biotechnology, self-assembling monolayers and multilayers are becoming increasingly important as technological tools in production of mono-molecular devices. These encourage a development of new techniques for thin film measurement.
U.S. Pat. No. 6,545,763 (Kim et al.) discloses a method and a recording medium for measuring three-dimensional thickness profile and refractive index of a transparent dielectric thin-film with or without a pattern, which is fabricated in the semiconductor or related industrial field. A method for measuring a thickness profile using white-light scanning interferometry in an optical system includes the following steps. A first step extracts a phase graph by acquiring an interference signal and performing Fourier transform. A second step is to extract a mathematical phase graph through modeling of a measurement object. And a third step is to measuring a profile value and a thickness value by applying an optimization technique to an error function determined by using phase values which is acquired from said first step and said second step.
In U.S. Pat. No. 5,748,296 (Canteloup) is described an illumination beam that is sent onto a localized region of the surface layer of a thin-film structure which is being etched in a vacuum processing chamber. The reflected light beam is sent through a filter to the matrix sensor of a video camera, and to an optical disperser or an interference filter, a selection diaphragm, a fiber-optic cable, and an analysis slit at the input of the optical disperser or interference filter. A spectral analysis of the reflected light beam is performed to determine the layer structure of a localized region.
U.S. Pat. No. 5,729,343 (Aiyer) disclosed a film measurement apparatus having a stage with a support surface on which a substrate coated with a film may rest. An extended light source faces the stage, and an imager is aimed at the stage to capture the reflection of the light source. The imager includes a receiver upon which an image of an extended portion of the substrate may be generated, and a processor in communication with the imager is operated to calculate the thickness of the film at a plurality of locations. The stage may be tilted to empirically measure an average illumination and the contrast between interference fringes, avoiding theoretical estimates provided by Fresnel's equation.
U.S. Pat. No. 6,182,512 (Lorraine) described imaging apparatus, which includes a wave generator for generating a wave in an article; a detector for detecting a wave in the article; and a processor which carries out several functions. It forms a matched filter based on a response of the article to a wave propagated through the article; it directs the wave generator to generate a wave at a plurality of generation positions; it directs the detector to detect a motion of the article at a plurality of detection positions; forms a scan data set from the detected motion of the article; it multiplies the scan data set by the matched filter to produce a compensated data set; and coherently sums data points in the compensated data set to produce a focused image.
In U.S. Pat. No. 5,999,262 (Dobschal et al.) a process and a device are described for detecting physical, chemical, biological or biochemical reactions and interactions on biochemically or chemically functionalized specimen carriers in the form of layers or films from the spectral reflection after irradiation of the specimens with light of different wavelengths. According to the process, the specimens are arranged on a substrate plate with a carrier layer of a carrier plate and are irradiated with light. The following process steps are carried out: a) temporally resolved illumination of a local arrangement of specimens to be analyzed by light of different wavelengths from a tunable light source which is arranged subsequent to a polychromatic light source; b) the imaging of the beam component reflected from at least one boundary surface of each specimen or of the beam components or interferences reflected and interfered, respectively, at boundary surfaces of each specimen which are arranged one behind the other in the direction of light, this imaging being carried out on a spatially resolving areal detector array or a video camera by means of subsequently arranged optical elements; and c) a wavelength-selective detection of the radiation intensities reflected and influenced by the specimens or of the intensities of the imaged interferences, determination of a wavelength spectrum associated with each specimen, and derivation of parameters characterizing the interactions and reactions to be analyzed.
U.S. Pat. No. 5,440,238 discloses apparatus and method for detecting, determining, and imaging surface resistance corrosion, thin film growth, and oxide formation on the surface of conductors or other electrical surface modification. The invention comprises a modified confocal resonator structure with the sample remote from the radiating mirror. Surface resistance is determined by analyzing and imaging reflected microwaves; imaging reveals anomalies due to surface impurities, non-stoichiometry, and the like, in the surface of the superconductor, conductor, dielectric, or semiconductor.
U.S. Pat. No. 5,133,601 describes an invention relates to an interferometric measuring device capable of profiling a surface with large height variations.
Briefly described, and in accordance with one embodiment thereof, the invention provides a method of profiling a rough surface of an object by producing an optical path difference so that initially a highest point of the rough surface is optically aligned with and outside of the focus range of a solid-state imaging array.
The contrast or modulation for each pixel is determined from the intensity data. That contrast or modulation is compared with a stored prior value of contrast or modulation of that pixel. The prior value is replaced with the most recently computed contrast or modulation if the most recently computed one is greater than the one previously stored. The corresponding relative height or optical path difference is also stored for that pixel. The optical path difference is either incrementally or linearly varied through a selected distance, and the foregoing procedure is repeated until maximum values of contrast are obtained and stored for each pixel.
The present invention aims at providing a new compact optical tool for measurement of atomically thin films, which can give a real time image thickness map with high spatial resolution. It also opens the possibility of working with transparent substrates commonly used in biology. Current thin film measurement methods do not possess such a universal appeal.